A number of methods have been used to obtain a color positive directly on a photosensitive material from a color original. Typically, light from a halogen lamp or the like is cast on a color original, and the reflected light or transmitted light is focused with a lens or the like onto the surface of a photosensitive material for exposure. Then, development is performed to obtain a positive. The color original includes, for example, a transmission type, such as a color slide or a motion picture positive film, and a reflection type, such as a color print, color-printed matter, an illustration and a painting. The photosensitive material is one used in a process for obtaining a positive directly, including a reversal material, such as color reversal film, color duplicating film or color reversal paper; an autopositive material, such as autopositive color film or autopositive color paper; and a diffusion transfer material, such as instant film or diffusion transfer type dry color paper. For these types of materials, the following two processes have been mainly used to adjust the color balance of the resulting positive image. The first is the additive color process, in which light is divided into the three primary colors, blue, green and red, and exposure is performed three times. Because of the necessity for three separate exposures, this process is complicated and poor in productivity; however, it provides a positive satisfactory in color separation and color reproduction. The other process is the subtractive color process, in which cut-filters for yellow, magenta and cyan are inserted somewhere in the optical system, and the color balance is adjusted by adjusting the amount of exposure. With this process, exposure is performed once, the instruments and procedure are simple, and the printing time is short. Despite these advantages, it involves the disadvantages that color separation and color reproduction are poor.
With the subtractive exposure process, therefore, a method of forming a color image with good color separation and good color reproduction is desired. To attain this purpose, it has been suggested to sharpen the spectral sensitivity distribution of the photosensitive material to blue, green and red colors, thereby raising the accuracy of color separation with which to duplicate color density from the original.
There have been attempts to sharpen the spectral sensitivity distribution of a photosensitive material by incorporating a suitable light-absorbing dye therein [JP-B-51-1419 (corresponding to U.S. Pat. No. 3,746,539), JP-A-52-20830 or JP-A-57-112750 (The term "JP-A" as used herein refers to a "published, unexamined Japanese patent application", and the term "JP-B" as used herein refers to an "examined Japanese patent publication")]. In a negative printing process, there have also been attempts to sharpen spectral sensitivity with the use of an external filter (JP-A-53-64037, JP-A-51-113627).
The incorporation of a light-absorbing dye in a photosensitive material, however, has the disadvantage that the absorption spectrum of the dye is too broad, and the dye absorbs light in the region that should be transmitted, thereby lowering the spectral sensitivity of the photosensitive material. The method involving the use of an external filter relates to a negative printing process rather than a positive-positive printing process in which a color positive is obtained directly from a color original. Color reproduction in a positive-positive printing process is difficult compared with a negative-positive process. With a negative-positive process, materials for use in printing are all negative films, and images are composed mostly of azomethine dyes (coupling products of couplers with developing agents). The range of tolerance for the spectral sensitivity of the photosensitive material to be printed on, therefore, is relatively broad. In the case of a positive-positive process, by contrast, the original is a transparency positive, a coupler-in-developer type color slide film or a coupler-in-emulsion type color slide film, all widely different in dyes to be developed. Reflection-type positive originals include a wide variety of materials, such as color picture prints, printed matter, paintings, illustrations, and real objects. The coloring materials making up the image are widely varied, including azomethine dyes, azo dyes, organic pigments and inorganic pigments. The absorption spectrum for each of them cannot be restricted to yellow, magenta or cyan with a virtually single spectrum as in the case of a negative film. The faithful reproduction of the original that uses these various coloring materials is a very difficult task with a photosensitive material for obtaining a direct color positive.